Recent research in East Africa has established the existence of significant indigenous MSM networks, characterized by apparently high HIV seroprevalence rates and high stigma. We propose a mixed methods study (qualitative, quantitative, and biological STI/HIV markers) to study 350 MSM in Dar es Salaam (high HIV prevalence) and Tanga (lower prevalence), Tanzania, where there are no available data on MSM. The study will map sexual meeting places for MSM, elicit information on the level and experience of stigma, the process by which stigma is translated into HIV risk behavior, and health care experiences and needs of MSM. Quantitative data on demographics, sexual pathways and risk behaviors, sexual contacts, internalized homophobia, and context of sexual behavior, will be collected using a modified version of the MSM questionnaire recently used in Kampala. Linked to this will be biological data on HIV, syphilis and urethral and rectal gonorrhea and Chlamydia. Respondents testing positive for treatable STIs will be treated immediately, and for HIV referred to the free treatment program at Muhimbili Hospital. We will assess demographic and behavioral predictors of HIV and STIs, sexual risk behaviors with males and females and their context, and the impact of stigma on risk (or protective) behaviors. The emerging description of sexual risk, stigma, and HIV/STI prevalence will be used to inform a subsequent R01 to intervene to reduce risk and provide culturally sensitive health care for MSM in Tanzania, and design and implement a model program that can be used more broadly in East Africa. PUBLIC HEALTH RELEVANCE: We will study HIV and SDI prevalence in high-risk men in Dar es Salaam and Tanga, Tanzania, to assess what behaviors are most closely associated with HIV and STI infection in both cities. We will also interview these men to determine what role stigma related to their sexual activities plays in reducing HIV testing, and how interventions to reduce HIV risk and improve health service access in this population might be structured.